Buffers are frequently used to provide isolation and/or gain between two electronic circuits. A single emitter-follower stage is an example of a very simple buffer.
More complex buffers are frequently required in situations where the buffer must have high current drive capabiities and yet exhibit low noise characteristics. Such high current/low noise buffers are available in bipolar form, but they are more difficult to build using CMOS or NMOS technology, primarily because of the difficulty in obtaining low noise and high current drive in MOS devices. Nevertheless, MOS-type buffers having high current drive and low noise capability are very desirable for certain applications.
Another desirable feature in the type of MOS buffer to which this invention is addressed is the ability to switch from a high current drive condition to a lower current drive/low noise condition as circumstances permit, thereby to reduce the current drain on the buffer's power supply. Of course, switching between these conditions must ordinarily be accomplished without a noticeable effect on the buffer's output signal. Conventional MOS-type buffers have simply not been able to provide this feature by using any commercially practical design.